The public are being urged to boycott the census in Scotland over allegations that the parent company of a UK firm contracted to gather information has been linked to the torture of prisoners at Iraq's notorious Abu Ghraib prison.Protesters say they are willing to break the law and face a criminal record and a £1,000 fine in an attempt to force the Scottish government to cancel the £18.5m contract it awarded to CACI (UK).

The London-based company is a wholly-owned subsidiary of US contractor CACI International, which provided interrogators who worked at Abu Ghraib prison at the height of the prisoner abuse scandal. The prison became infamous in 2004 when disturbing images emerged of US soldiers abusing prisoners. The pictures included naked Iraqi detainees cowering from dogs, and US soldiers were later found to have perpetrated widespread torture.

Civilian staff working for private US security companies specialising in interrogation techniques were alleged to have been involved in some of the human rights abuses.In August 2003, CACI International provided staff to the US army to conduct IT and intelligence work in Iraq, including interrogation services. The company denies allegations that any of its staff were involved in assaults and has defended itself in US courts against lawsuits brought by a number of former prisoners.

In Scotland, the campaign against CACI is being led by a civil liberties organisation called Scotland Against Criminalising Communities (SACC).Richard Haley, the chairman of SACC, said the Scottish government should cancel the contract with CACI and hire another firm. "Of course, postponing the census would be disruptive," he said. "But anything would be better than continuing with the unethical arrangements that the Scottish government seems to believe it is stuck with.

"It's a matter of record that staff employed by CACI International interrogated people detained without charge at Abu Ghraib. They did so under US rules of engagement that permitted sleep deprivation, sensory deprivation and intimidation by dogs. SACC believes detention and interrogation in these circumstances violate international human rights norms. If the Scottish government won't cancel the contract, I hope that people in Scotland will use census day to say 'no' to this dirty business."

Householders are legally obliged to complete and return census forms and could face fines of up to £1,000 if they refuse, but SACC said the risk of prosecution is "slight". Haley said that people angered at CACI's involvement could also choose to supply inaccurate information and that SACC is asking researchers to boycott data obtained in the survey.

Some 6,000 temporary staff are being recruited to carry out the population survey in Scotland on 27 March. Questionnaires will be delivered to 2.5 million households.CACI's contract is to run the census for the General Register Office of Scotland (GROS) and process the population's responses. The company said it took the Abu Ghraib allegations extremely seriously and that it did not condone illegal behaviour by any of its employees.

A statement said: "In spring 2004, an allegation was made that a CACI employee had been involved in the mistreatment of detainees at the Abu Ghraib prison in Iraq. This allegation was not substantiated by any evidence or proof at the time it was made and subsequent investigations by both CACI and the US government could not confirm it.

"No CACI employee was ever depicted in the shocking and disturbing photos seen in the press at the time. Seven years on, the allegation remains totally unfounded and unproven. No CACI employee has ever been charged with any wrongdoing. If an employee of CACI had been found to be involved in such behaviour, we would have taken swift and appropriate action. We have, and always will, hold ourselves to the highest ethical standards."

In the US, four Iraqis brought a federal lawsuit against CACI International asserting that its staff participated in torture at Abu Ghraib. Suhail Najim Abdullah al Shimari, Taha Yaseen Arraq Rashid, Sa'ad Hamza Hantoosh Al-Zuba'e and Salah Hasan Nusaif Jasim al-Ejaili were all detained in the prison after the 2003 US-led invasion.

They allege they were subjected to electric shocks, sexual assault, brutal beatings and mock executions. Rashid claims he was forcibly subjected to sexual acts by a female as he was cuffed and shackled to cell bars. He also alleges that he was forced to witness the rape of a female prisoner and had a taser gun fired at his head.

So far, the legal actions concern whether CACI has civil immunity. In 2009 the US court of appeals ruled that it fell under the US military chain of command and thus had government contractor immunity. The supreme court is considering the case. There has been no ruling on the actions of the CACI employees.